1. Field of The Invention
The present invention relates to a drive control device for an opening and closing member, and more particularly, to such a drive control device which is equipped with a safety mechanism by which undesirable pinching of a foreign object, by the opening and closing member under closing movement thereof, can be prevented.
2. Description of The Related Art
As one of drive control devices of the abovementioned type, there is known a control device which controls a driving mechanism which, for opening and closing a window (viz., opening and closing member) of a motor vehicle, raises and lowers the window by the force of an electric motor. That is, when the motor is energized to run in one direction, the window is raised, while, when the motor is energized to run in the other direction, the window is lowered.
In conventional control devices, there is a type wherein while a window up switch is kept ON, the motor continues to run in one direction to close the window, and when the window up switch is turned OFF, the motor stops running. In these control devices, there is also a type which has means for monitoring whether, during upward movement of a window, a part of a passenger's body is accidentally pinched by the window or not. That is, if such pinch is detected, the motor is instantly switched OFF to stop upward movement of the window for increased safety. In such control devices, there is employed a system which monitors change in a closing resistance value (for example, driving current of the electric motor) which varies based on increase in resistance to rising movement of the window, and which, when the closing resistance value (which will be referred to as a watch value hereinafter) exceeds a predetermined threshold level, is active to stop rotation of the motor in the closing direction, judging that pinching has occurred due to the presence of an object blocking the path of closing movement of the opening/closing member.
In addition to the above-mentioned type of drive control device, there is another so-called `learning control` type in which a closing resistance of the window varies in accordance with the closing position thereof. The threshold level for pinch detection is set by memorizing the monitor value repeatedly and renewing the threshold level each time the window changes its closing position. For example, in case wherein pinch detection is intended by monitoring a change of the driving current of the electric motor, the monitor value detected under normal operation of the window is memorized for each closing position of the window and a predetermined allowed variation value is added to the memorized monitor value to make a threshold level for pinch detection for each closing position. When, thereafter, the window is moved in a closing direction, the detected monitor value for each closing position is compared with the threshold level to determine whether pinching has occurred. The value for deriving the threshold level is constantly renewed unless occurrence of pinching is detected.
However, in such a `learning control` drive control device, it is difficult to allow the threshold level for pinch detection to have a predetermined value which can be commonly used throughout full range of the closing movement of the window. That is, considering the closing resistance varies depending on the closing position of the window it is necessary to add a variation allowance to the threshold level. However, according to this necessity, the sensitivity of pinch detection must be lowered by a degree corresponding to the allowance.
In the latter drive control device, the threshold level for pinch detection is set in accordance with the closing position of the window. However, because in setting the threshold level the allowance added to the memorized monitor value is constant, a drawback is present in such types of drive control device. That is, the degree of allowance is varied in accordance with the degree of the memorized monitor value over the entire threshold. For example, in case wherein the closing load of the window is small and thus the monitor value is small, the degree of allowance is effectively larger and thus the sensitivity of pinch detection is lowered. While, in a case wherein the closing load is large and thus the monitor value is large, the degree of allowance is effectively smaller and thus erroneous determination of occurrence of pinching may take place.
An object of the present invention is to provide a drive control device for an opening and closing member, which can always accurately detect pinching by controlling the threshold level for pinch detection to an optimum degree of sensitivity.